Disc to 40 or 50, Dual spec to Shadow when you can. Start using shadow for questing probably around when you get Vampiric Touch. Use Disc to heal dungeons for instant queues.

Use standard glyphs except for these 2 which are amazing for questing
- Spirit Tap (regen mana after a kill)
- Psychic Scream (mobs do not scatter when you fear them, so you can use your fear liberally and not end up aggro'ing everything in the radius).